In the past, systems have been developed which employ a CRT, LCD or other display device as well as devices to identify a position on the display screen thereof. One such example is a shooting game device. In such a shooting game device, various means may be employed to identify a position on the screen. Of these, the technologies disclosed in Patent Document 1, Patent Document 2, and Patent Document 3, cause a screen to be displayed on a display device according to the game progress, based on display signals from a game apparatus; by operating a gun-type controller or other means for indicating a screen position, a user irradiates the screen periphery with light or emits light from a light-emitting member on the screen periphery, and based on image capture results at the screen periphery, identifies the position on the screen at which the screen position indication means is aimed.    Patent Document 1: Japanese Patent No. 3422383    Patent Document 2: Japanese Patent Laid-open No. 11-305935    Patent Document 3: Japanese Patent Laid-open No. 2004-139155
However, the system of the above-mentioned Patent Document 1 has the following problems.
(1) Detection errors cannot be ignored because the indicated position or other detected numerical value is an approximate solution.
(2) In the device manufacturing stage, adjustments must be made in order to determine constants necessary for position detection, so that manufacturing processes are complex, and there are concerns that adjustment errors may be reflected in detection errors during device operation.
(3) The four light-emitting members which identify the video screen are not distinguished. Hence, at least based on the description in Patent Document 1 alone, the top, bottom, right, and left of the screen cannot be identified.
(4) When an image of the four light-emitting members and other disturbing light sources is captured simultaneously, it is difficult to distinguish the light-emitting members from the disturbing light sources, so that severe limitations are placed on the peripheral illumination environment during device operation.
Moreover, in the system of Patent Document 2, only an indicated position and distance information are detected, but in contrast with the system of Patent Document 1, exact solutions can be obtained. However, this method has the following problems.
(1) The structure of computations is complex, and a large amount of computation is required.
(2) Errors in the focal length due to differences between device units have an adverse effect on computation results because the focal length of the lens comprised by the image capture element is used in computations.
(3) An infrared light source is used to identify the indication target plane, but the infrared rays are distinguished from disturbing light sources based on brightness alone, so that once again, severe limitations are placed on the peripheral illumination environment during device operation.
(4) The device configuration on the screen side is complex and related constraints are imposed because an infrared light source is used which itself emits light from the target screen side. As a result, such devices are not suitable for use in the home.
Moreover, in the system of Patent Document 3, which was presented by the applicant of this application, only a position indicated by a gun-type controller is detected. This is insufficient for implementing a more varied and sophisticated game, for example by obtaining the angle of rotation around the gun axis, the distance to the display device, and other relative position information, and so the range of application is limited.
Further, in technology of the prior art such as described above, there are also problems arising from the image capture element used in image capture. That is, when using generic image capture elements, if the object or the image capture element moves comparatively rapidly, the image of the object is blurred, and the expected image recognition result cannot be obtained, so that target screen identification may fail. As one method for resolving this problem, an image capture element with a fast shutter speed can be used. However, such fast image capture elements are expensive compared with the image capture elements in wide use.
This invention is presented in order to solve the above-described problems of the prior art, and has as a principal object the provision of a position information detection device, method, and program, capable of detecting with high precision various position information using simple and easily recognized discrimination marks.
A further object of the invention is to provide a position information detection device, method, and program, capable of improving the success rate of position detection, even when using an inexpensive image capture element.